Lacquer is an insoluble film layer that develops over metal surfaces when metal surfaces are contacted with oil based lubricant compositions. To control lacquer formation, dispersants are added to lubricant mixtures. Lacquer can cause wear of system components and an overall reduction in system performance. Unfortunately, the presence of dispersants in lubricants has the undesireable effect of facilitating the formation of stable water-in-oil emulsions. Water is an undesirable contaminant of lubricant systems as it reduces the effectiveness of lubricants by forming harmful by-products. These water-in-oil emulsions cause losses in system efficiencies because they do not transmit power as effectively as lubricants nor do they lubricate as effectively as needed. There is thus a need to improve the demulsification, i.e., watershedding, properties of oil based lubricants formulated with dispersants. Demulsification is the process by which unwanted water-in-oil emulsions are “broken up.”
In the prior art, many demulsifiers have been suggested and used. Demulsifier additives known in the art include but are not limited to derivatives of propylene oxide, ethylene oxide, polyoxyalkylene alcohols, alkyl amines, amino alcohols, diamines or polyamines reacted sequentially with ethylene oxide or substituted ethylene oxides or mixtures thereof. Examples of demulsifier additives include trialkyl phosphates, polyethylene glycols, polyethylene oxides, polypropylene oxides, (ethylene oxide-propylene oxide) polymers and mixtures thereof. U.S. Pat. No. 4,129,508 discloses the use of reaction products of a hydrocarbon substituted succinic acid or anhydride with one or more polyalkylene glycols or monoethers thereof to improve demulsification properties of lubricant and fuel compositions. U.S. Pat. No. 4,396,518 discloses an improved demulsification additive that is a combination of an acylated alkoxylated isopentylphenolic resin and a propoxylated-ethyoxylated amylphenolic resin. U.S. Pat. No. 5,753,598 discloses a combination of an epoxy-based demulsifier and a heterocyclic compound to improve water shedding properties in trunk piston oils. U.S. Pat. No. 6,255,263 discloses the use of at least one oil-soluble polyoxypropylene glycol monoalkyl ether to improve demulsification properties. U.S. Pat. No. 6,544,937 discloses a lubricating composition containing naphthenic basestocks having improved demulsification properties by the addition of a demulsification additive selected from oxyalkylated glycols, esters of oxyalkylated glycols and mixtures thereof. GB 2,265,149 discloses the use of at least one block copolymer or propylene oxide and ethylene oxide and at least one oxyalkylated amine to improve demulsification properties while not interfering with the effectiveness of rust inhibitors used.
Despite the advances in lubricant oil formulation technology, there remains a need for demulsifiers that effectively reduce the formation of emulsions in oil based lubricants formulated with dispersants added to minimize the formation of lacquer.